295.htm

unix高级编程原吗

            If the DATA MARK arrives before the INS, the serving site <br>
            should not process the data stream further until an INS is <br>
            received. <br>
   This approach to handling selected special characters or signals <br>
   relieves the using Telnet processes from having to recognize the <br>
   special serving site characters, as well as from having to know how <br>

   the serving site wants to handle them.  At the same time, the <br>
   procedure requires only a minimum level of user understanding of the <br>
   serving site.  This seems appropriate, since the Telnet ASCII <br>
   conventions are providing a Network Virtual Terminal, not a Network <br>
   Virtual User. <br>
   Notice that the correct order is (1) special character or signal <br>
   (e.g. BREAK or <etx>), then (2) SYNCH. <br>
User Telnet Signals <br>
   The ability of the user to cause the using site Telnet to send any <br>
   combination of ASCII characters in a string, and only that <br>
   combination, is viewed as important to the user utility of the Telnet <br>
   ASCII conventions.  Because of this, some user sites may find it <br>
   necessary to provide special local Telnet signals from the human user <br>
   to the using site Telnet. <br>
      Example: <br>
      A user on a line at a time system (Multics, System 360, GCOS, <br>
      etx.), which require an end of line signal before processing the <br>
      user's input, is working through the Network on a serving site <br>
      that operates a character at a time.  The application is a <br>
      debugging aid that permits the user to type in "location=" to <br>
      which it will respond with n where n represents the current <br>
      contents of that location.  The serving site process does not <br>

      expect to see the "location=" followed by a carriage return line <br>
      feed sequence.  The user at the using site should be able to type <br>
      in the location, follow it with a signal (to the user Telnet) to <br>
      suppress the end of line convention, followed by the end of line <br>
      signal, and expect the "location=" to be transmitted immediately <br>
      without an end of line sequence being transmitted to the server. <br>
Postel                                                         [Page 13] <br>
RFC 318                     Telnet Protocol                   April 1972 <br>
      Example: <br>
      In another case, a using site has decided that it is convenient to <br>
      accumulate four characters at a time and transmit them to the <br>
      serving site, unless an end of line signal is observed, in which <br>
      case the end of line sequence is sent preceded by whatever number <br>
      of characters have been accumulated (presumably three or less). <br>
      In the same debugging application, the address is such that the <br>
      end does not correspond with the four character buffer <br>
      demarcation.  The user should have the ability to enter a code for <br>
      "transmit immediately" in place of the end of line signal in order <br>
      to preserve neat formatting, and expect the address to be sent to <br>
      the serving site. <br>
   Telnet Signals have been discussed and those introduced to date are <br>
   probably sufficient for an implementation of Telnet ASCII convention. <br>

Terminology <br>
   ASCII          - The USASCII character set as defined in NIC # 7104. <br>
                    In Telnet Protocol, where eight bit codes are used <br>
                    the lower half of the code set is defined to be <br>
                    ASCII. <br>
   echoing        - The display of a character entered is called echoing. <br>
                    There are two modes in which this happens.  If <br>
                    the device used to enter characters displays the <br>
                    character before (or as) it transmits the character <br>
                    to the computer the echoing mode is called "local <br>
                    echo."  If, on the other hand, the device transmits <br>
                    the entered character to the computer without <br>
                    displaying it and the computer then transmits a <br>
                    character to the device for the echo display, this <br>
                    echoing mode is called "remote echo." <br>
   character mode - In this mode of operation Telnet transmits each <br>
                    character as soon as possible.  Generally speaking, <br>
                    character mode is used when all of the using terminal, <br>
                    using system, and serving system are operating <br>
                    in a remote echo mode.  The echos to the user <br>
                    entered characters are transmitted from the serving <br>
                    system (i.e., over the network). <br>

   line mode      - In this mode of operation Telnet transmits groups <br>
                    of characters which constitute lines.  Generally <br>
                    speaking, this mode is used when one or more of <br>
                    the using terminal, using system, or serving <br>
Postel                                                         [Page 14] <br>
RFC 318                     Telnet Protocol                   April 1972 <br>
                    system is operating in a local echo mode.  The <br>
                    echos to the user entered characters are not <br>
                    transmitted over the network). <br>
   full duplex    - This term indicates a transmission procedure using <br>
                    a four wire connection, which permits simultaneous <br>
                    transmission in both directions. <br>
   half duplex    - This term indicates a transmission procedure using <br>
                    a two wire connection, which requires that data be <br>
                    transmitted in only one direction at at time. <br>
   Note that half duplex devices usually are also local echo but that <br>
   full duplex devices may be either local echo or remote echo. <br>
IV.  PROPOSED CHANGES TO TELNET PROTOCOL <br>
   The changes suggested here are not my ideas, thus the presentation may <br>
   be faulty.  I welcome RFC or other communication suggesting other <br>
   changes or better arguments for and against these changes. <br>
Echoing <br>
Echoing <br>
   It is proposed to delete from Telnet the control signals ECHO, NOECHO, <br>
   and HIDE YOUR INPUT.  For Server systems which do not provide echoing, <br>
   these commands are useless.  For server systems which do provide <br>
   echoing experience has shown that the control is most effectively <br>
   provided by server system commands. <br>
Data Types <br>
   It is proposed to delete all mention of data types from Telnet. <br>
   Either the character stream is ASCII or its not a Telnet <br>
   communication.  If it is really necessary to change the data type, a <br>
   command in ASCII could be sent in the data stream. <br>
Minimum Implementation <br>
   It is proposed that the minimum implementation require the user Telnet <br>
   to allow the user to send and the server Telnet to correctly process <br>
   all the Telnet control signals. <br>
Postel                                                         [Page 15] <br>
RFC 318                     Telnet Protocol                   April 1972 <br>
   The  work on Telnet Protocol has involved many people.  This document <br>
   is taken from RFC's #139 and #158 by Tom O'Sullivan.  Others who <br>
   have served on committees are: <br>
                    Bob Bressler           MIT-DMCG <br>
                    Will Crowther          BBN <br>
                    Bob Long               SDC <br>

                    Alex McKenzie          BBN <br>
                    John Melvin            SRI-ARC <br>
                    Bob Metcalfe           MIT-DMCG <br>
                    Ed Meyer               MIT-Multics <br>
                    Tol O'Sullivan         Raytheon <br>
                    Mike Padlipsky         Mit-Multics <br>
                    Jon Postel             UCLA-NMC <br>
                    Bob Sundberg           Harvard <br>
                    Joel Winett            LL <br>
                    Steve Wolfe            UCLA-CCN <br>
        [This RFC was put into machine readable form for entry] <br>
     [into the online RFC archives by Kelly Tardif, Viaginie 10/99] <br>
  <br>
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